IMMUNOHISTOCHEMICAL LOCALIZATION OF A GAP JUNCTION PROTEIN (CONNEXIN43) IN THE MUSCULARIS EXTERNA OF MURINE, CANINE, AND HUMAN INTESTINE

Electron-microscopic studies have revealed a heterogeneous distributio n of gap junctions in the muscularis externa of mammalian intestines. This heterogeneity is observed at four different levels: among species ; between small and large intestines; between longitudinal and circula r muscle layers; and between subdivisions of the circular muscle layer . We correlated results obtained with two immunomethods, using an anti body to the known gap-junctional protein (connexin43) with ultrastruct ural findings, and further evaluated the respective sensitivity of the se two approaches. For comparative reasons we also included the vascul ar smooth muscle of coronary arteries into our study. Two versions of the immunotechnique (peroxidase-antiperoxidase and fluorescence method s) were applied to frozen sections of murine, canine, and human small and large intestines, as well as to pig coronary artery. In the small intestine of all three species a very strong reactivity marked the out er main division of the circular muscle layer, while the longitudinal muscle layer as well as the inner thin division of the circular muscle layer were negative. In murine and human colon both muscle layers wer e negative, while in canine colon the border layer between the circula r muscle and the submucosa reacted strongly, and scattered activity wa s found in the portion of the circular muscle layer (one tenth of its thickness) closest to the submucosa. The remainder of the circular mus cle layer and the entire longitudinal muscle layer were negative in th e canine colon. In the coronary artery we could not confirm the positi ve, specific labeling reported by other investigators (l.c.). In concl usion, we found close correlations at all four above-mentioned levels in the distribution of gap junctions in the gut musculature, as determ ined by binding of anti-connexin43 in comparison to conventional ultra structural studies. Since no significant immunostaining was found in ( i) the outer border of the circular muscle layer of the canine colon a nd (ii) the border layer between the submucosa and the circular muscle layer of human colon, where rare gap junctions have been identified a t the ultrastructural level, we conclude that the electron-microscopic analysis is the more sensitive of the two methods.